In an optical module such as a light transmitting and receiving module in which light-emitting elements (semiconductor lasers) and light-receiving elements (photodiodes) are disposed in one housing, suppression of optical crosstalk has been quite an important factor to obtain good light receiving sensitivity. As the causes of the optical crosstalk, there exist mainly two paths as follows. The first path is such that light emitted from a light-emitting element is scattered by inner walls of the housing and then reaches a light-receiving element. The second path is such that light leaked from an active layer of the light-emitting element (semiconductor laser) into a substrate (to be referred to as leakage light hereafter) is emitted from a side wall of the light-emitting element into the outside and then directly reaches the light-receiving element or is scattered by the inner walls of the housing and then reaches the light-receiving element. To suppress the optical crosstalk, various methods have been conventionally devised.
For example, Patent literature 1 describes an optical module in which a light-emitting element and a light-receiving element are mounted on a substrate and a wavelength-selecting filter is inserted between the light-emitting element and the light-receiving element to reflect stray light from the light-emitting element, to thereby suppress optical crosstalk.
Also, Patent literature 2 and Patent literature 3 describe an optical module in which a plurality of optical semiconductor elements are mounted on a substrate and a light-absorbing resin (or light shielding resin) is arranged between the plurality of optical semiconductor elements to form a configuration to suppress optical crosstalk between the elements in which, after peripheral areas of the optical semiconductor elements are covered with a transparent resin, the surface of the substrate including the transparent resin is coated with the light-absorbing resin (or the light-shielding resin).